[gmx-users] a question about removing the rotation

David spoel at xray.bmc.uu.se
Fri Oct 17 22:05:01 CEST 2003

On Fri, 2003-10-17 at 21:40, Wei Zhang wrote:
> Dear David,
> I read the code calculating the inertia momentum. I don't understand in a place.
> I think the inertia momentum should be calculated like:
> Ixx = sum( m(i)*(y(i)^2+z(i)^2 )
> Iyy = sum( m(i)*(z(i)^2+x(i)^2 )
> Izz = sum( m(i)*(x(i)^2+y(i)^2 )
> But in gromacs code, there is 
> 	/* Update inertia tensor */
> 	update_tensor(x[i],m0,vcm->group_i[g]);

Maybe the comment is not entirely up to date, but a bit further down we
do a matrix inversion (line 257) for the inertia tensor. I have also
tested the code, but please do some tests yourself to see whether it
works correct (in the comment it says it even works in parallel!)

David van der Spoel, PhD, Assist. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel

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